The present invention relates to power steering systems for vehicles, and more particularly to an energy saving control system and method for an electro-hydraulic power steering system for a hybrid vehicle.
Vehicles including hybrid powertrains incorporate two or more devices for powering the vehicle. For example, hybrid vehicles often include an internal combustion engine (ICE) or a diesel engine as a primary power source. An electric machine such as an integrated flywheel alternator stator or an electric motor are often used as a secondary power source. These hybrid vehicles also usually include an electro-hydraulic power steering system that provides power assisted steering and braking.
The electro-hydraulic power steering system typically includes an electric motor that rotates an input shaft of a hydraulic pump. The electric motor is powered by batteries or an alternator depending upon which power source is currently active. The hydraulic pump supplies pressurized hydraulic fluid to a brake booster. Hydraulic pressure from the hydraulic pump is also used to assist the movement of a steering gear, which turns the wheels of the vehicle. Hydraulic fluid from the steering gear is returned to a reservoir that is connected to the hydraulic pump.
A primary goal of the hybrid powerplant is to improve the energy efficiency of the hybrid vehicle. Reducing the energy consumption of major power-consuming components in the hybrid vehicle is necessary to achieve this goal. The electro-hydraulic power steering system is a major vehicle component that consumes a significant amount of power.
To reduce the power consumption of the power steering system, an electro-hydraulic power steering system with a closed center valve and a high-pressure accumulator has been proposed. This power steering system attempts to reduce energy consumption during non-steering conditions. This system, however, reduces steering performance, increases packaging requirements, reduces reliability and response times, and increases system complexity and cost.
An electro-hydraulic power steering system and method for a hybrid vehicle includes an electric motor and a hydraulic pump that is coupled to the electric motor. A first controller communicates with the electric motor, selects one of a plurality of operating modes of the electro-hydraulic power steering system and applies power to the electric motor based on the selected one of the operating modes.
In other features, the operating modes include Standby, On and Off operating modes. The first controller turns the first controller off and the electric motor off when in the Off operating mode. The first controller turns the electric motor off and the first controller on when in the Standby operating mode. The first controller turns the electric motor on and the first controller on when in the On operating mode.
In other features, the first controller selects the On operating mode when a gear selector of the hybrid vehicle is not in park and an ignition switch is in a Run position after passing through a Start position. The first controller selects the Off operating mode when an ignition switch of the hybrid vehicle is in an off/lock position. The first controller selects the Standby operating mode when the ignition switch of the hybrid vehicle is an accessory position.
In yet other features, when the first controller selects the Standby operating mode, the first controller switches to the On operating mode when at least one of steering and brake input occurs. The first controller returns the electro-hydraulic power steering system to the Standby mode after a first period if additional brake and steering inputs do not occur.
In other features, when an electric power takeoff (EPTO) mode of the hybrid vehicle is selected, the first controller selects the Off operating mode.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.